1. Field of the Invention
This invention relates to a PN or PIN junction type semiconductor photoelectric conversion device which is of particular utility when employed in a solar battery.
2. Description of the Prior Art
A PN or PIN junction type semiconductor photoelectric conversion device is, in principle, provided with a semiconductor layer having formed therein at least one PN or PIN junction, a light-transparent, conductive layer deposited on the semiconductor layer and a conductive layer deposited on the semiconductor layer on the opposite side from the light-transparent, conductive layer; and the PN or PIN junction type semiconductor photoelectric conversion device is arranged so that when light is incident to the semiconductor layer from the outside of the light-transparent, conductive layer, a photoelectric conversion function is provided by the presence of a barrier which is set up by the PN or PIN junction.
In such a conventional PN or PIN junction type semiconductor photoelectric conversion device, there is interposed between the semiconductor layer and the light-transparent, conductive layer a layer which is formed unartificially during the deposition of the light-transparent, conductive layer on the semiconductor layer and which is formed of an oxide of the semiconductor forming the semiconductor layer and has a sufficiently small thickness to permit the passage therethrough of a current. Since the semiconductor layer is usually formed of silicon, the abovesaid layer sandwiched between the semiconductor layer and the light-transparent conductive layer is usually formed of a silicon oxide.
Such an oxide layer interposed between the semiconductor layer and the light-transparent, conductive layer has active oxygen, and hence is unstable chemically. Accordingly, the oxide layer, when heated, is liable to chemically react with the semiconductor layer, the light-transparent, conductive layer and an undesirable impurity from the outside. On the other hand, the PN or PIN junction in the semiconductor layer is formed as close to the light-transparent, conductive layer as possible so as to provide for enhanced photoelectric conversion efficiency.
Accordingly, the conventional PN or PIN junction type photoelectric conversion device has the defect that when it is exposed to high temperature for a long time, the thickness and height of the barrier set up by the PN or PIN junction varies, resulting in degraded photoelectric conversion characteristic and lowered photoelectric conversion efficiency.
In general, the oxide layer has a large energy band gap and when the oxide layer is a silicon oxide layer, the energy band gap is as large as 8 eV.
Consequently, even if the oxide layer interposed between the semiconductor layer and the light-transparent, conductive layer is so thin that a current may pass through the oxide layer, the layer itself does not readily permit the passage therethrough of a current and has a high resistance.
Accordingly, the prior art PN or PIN junction type semiconductor photoelectric conversion device has the defects of poor photoelectric conversion characteristic and very low photoelectric conversion efficiency.
Furthermore, in the conventional PN or PIN junction type semiconductor photoelectric conversion device, even if the oxide layer is interposed between the semiconductor layer and the light-transparent, conductive layer, the oxide layer is likely to pass an undesirable impurity from the light-transparent, conductive layer or the outside thereof to the semiconductor layer and an useful impurity introduced in the semiconductor layer to the light-transparent, conductive layer.
As a consequence, the conventional PN or PIN junction type semiconductor photoelectric conversion device is defective in that in a long use, the photoelectric conversion characteristic is deteriorated and, in particular, the photoelectric conversion efficiency is lowered.
Moreover, since the oxide layer interposed between the semiconductor layer and the light-transparent, conductive layer is formed unartificially, there is the possibility of the oxide layer being formed so thick as not to permit the passage therethrough of a current.
Accordingly, the prior art PN or PIN junction type semiconductor photoelectric conversion device has the drawback that difficulties are involved in its manufacture.